drm/msm/dpu: decide right side per last bit

drm/msm/dpu: decide right side per last bit

Currently, only one pair of mixers is supported, so a non-zero counter
value is sufficient to identify the correct mixer within that pair.
However, future implementations may involve multiple mixer pairs. With
the current implementation, all mixers within the second pair would be
incorrectly selected as right mixer. To correctly select the mixer
within a pair, test the least significant bit of the counter. If the
least significant bit is not set, select the mixer as left one;
otherwise, select the mixer as right one for all pairs.

Signed-off-by: Jun Nie <jun.nie@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/669226/
Link: https://lore.kernel.org/r/20250819-v6-16-rc2-quad-pipe-upstream-v15-3-2c7a85089db8@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>